Abstract: Basement membranes (BMs) are extracellular matrices (ECMs) containing laminins, collagen-IV, nidogens and proteoglycans as structural elements. They provide mechanical support for cells and act as signaling platforms. Laminins mediate BM assembly by adhering to cells, by establishing cytoskeletal links through receptors, by polymerizing, and by recruiting the other BM components. These cell-adherent ECMs are essential for tissue growth, differentiation, and maintenance, attributes that depend upon BM molecular architecture and receptor-binding. Diseases of BMs can result from structural changes that adversely affect muscle, peripheral nerve, kidney and other organs. The long-term goal of the grant is to elucidate mechanisms of BM assembly and architecture-dependent functions. This goal is critical for understanding BM disease pathogenesis and for developing therapies for BM defects. We now seek to determine how BMs can be modified to regain lost function in neuromuscular and renal diseases, explore the molecular basis of laminin polymerization, and elucidate architectural properties of BMs that determine functions. Aim I. Mutations ablating the polymerization laminin ?2 subunit result in ambulatory muscular dystrophy (LAMA2-MD) with peripheral nerve amyelination. We succeeded in ameliorating the muscle component of a mouse (dy2J) model of polymerization-deficient dystrophy by transgenic muscle expression of a laminin- binding linker-protein called ?LNNd. This leads us to evaluate this protein for repair of the peripheral nerve component of the disease. The aim holds potential for development of a therapy by viral somatic gene delivery. Aim II. Proteins conferring polymerization (?LNNd) and dystroglycan (?DG) receptor-binding (miniagrin, mag) to laminins have been used to ameliorate the severe muscle disease resulting from absent laminin-?2 (dy3K mice). The benefit results from modification of compensatory ?4 laminin that otherwise neither polymerizes nor binds to ?DG. Normal assembly and functions of ?4-laminins will be explored, focusing particularly on peripheral nerve myelination. We plan to complete an analysis of transgene muscle expression in the dy3K mouse, and evaluate ?LNNd and mag in Lm?2-null peripheral nerve to determine if this ameliorates the paresis. The aim is expected to elucidate laminin contributions needed for myelination and contribute to development of a therapy to treat muscle and nerve in LAMA2-MD arising from total loss of the ?2 subunit. Aim III. BM-binding proteins can be engineered to alter BM assembly and functions by increasing receptor binding, inducing polymerization, and altering inter-component binding and spacing. We propose to use these unique reagents to determine if the human laminin mutations that cause dystrophies and renal Pierson syndrome are due to failures of laminin polymerization, to map the polymerization residues on laminin LN domain surfaces accompanied by a structural analysis of the polymer node, probe the separate roles of laminin and collagen-IV polymers on cells, and evaluate inter-laminin spacing of the polymer in determining functions.